Humans aren't the only ones who experience midlife crises. ThinkStock/iStockphoto

January 29, 2013

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A committee from the National Institutes of Health recently recommended that scientists retire a majority of the chimpanzees currently being used for federally-funded medical research in the United States. The recommendation comes after a groundbreaking 2011 report from the Institute of Medicine that said such research is harmful to the animals and largely unnecessary. The NIH owns roughly 360 chimps, and the report suggests all but 50 of them ought to be sent to a national sanctuary. But while animal activists are rejoicing, others wonder if the cutback will come at the cost of advances in medical research. Wherever you stand on that argument, it's worth taking a look back at some of the things we've learned by studying chimps, monkeys, and other non-human primates over the years. The methodology of some research is unsettling — but the conclusions do lead to a better understanding of who we are.

1. Stress early in life can lead to drinking later in lifeThis is, perhaps, not a huge surprise, but at least now you know you can blame your childhood for your drinking habits. Researchers compared the alcohol consumption of two different groups of rhesus monkeys, one raised without adult contact and comfort, and another raised with their mothers. When the monkeys were roughly 4 years old, they were given access to alcohol, and the monkeys raised away from their mothers drank more alcohol more often than the mother-reared monkeys. Of course, even those of us with the most stable childhoods can be driven to drink. When the mother-reared monkeys were placed in stressful situations, they increased their alcohol consumption, too.

2. Birth control for men is on the horizonA 2004 study shed light on a potential new birth control option for men. Researchers gave nine male macaque monkeys booster shots of Eppin. This particular protein is found in the testes, and is added to the surface of sperm to protect them as they age. By giving the monkeys shots of synthetic Eppin, the researchers essentially vaccinated the monkeys against the protein. As a result, seven of the nine monkeys became infertile. When the shots stopped, five of the monkeys became fertile again within months. The fact that the other two didn't probably speaks to why this technique hasn't made its way into your local pharmacy yet, but it's a start.

3. The pill doesn't cause weight gainAnother study tested oral contraceptives on rhesus monkeys and found that, contrary to common belief, the pill could actually lead to weight loss in the obese. Both obese and average-sized monkeys took continuous daily human doses of oral contraceptives for eight months. At the end of the study, the obese monkeys had lost 8.58 percent of their body weight. The average-sized monkeys lost weight as well, but not nearly as much. While the study doesn't necessarily mean the pill should be used for weight loss, it "suggests that worries about weight gain with pill use appear to be based more on fiction than on fact," said senior study author Judy Cameron.

4. Eating less doesn't increase lifespanFor 25 years, researchers kept a group of rhesus monkeys on a low-calorie diet with hopes of proving that a restricted diet leads to longer life. According to the New York Times, "the males' weights were so low they were the equivalent of a 6-foot-tall man who tipped the scales at just 120 to 133 pounds." But when the study finally came to a close last year, the results were clear: The skinny monkeys died at around the same time as those that ate normally. Overall, a sad ending for the monkeys that spent their entire lives hungry, and for the researchers, some of whom had such high hopes that they started restricting their own diets.

5. We're not the only primates capable of selfless actsCan non-human primates experience empathy? Can they understand and share in another's feelings? Research suggests it's very possible. In one 1964 study, a group of six rhesus monkeys were taught to pull a chain to receive a helping of food. At one point, a seventh monkey was introduced to the group, and each time the first six pulled the lever for food, the new guy would get a painful electric shock. In response, the monkeys did one of two things: Some pulled a separate chain that administered less food, but didn't shock their companion. Others stopped eating entirely. One monkey went 12 days without eating to ensure it did not shock the others.

6. And we're not the only ones who have midlife crisesMany people encounter a dip in happiness around age 50, and may grapple with the sudden urge to buy incredibly expensive cars or join a rock band. An international team of researchers wanted to better understand the origins of the midlife crisis, so they turned to chimpanzees. By studying 500 of the primates, they found apes often go through a midlife crisis as well, experiencing a drop in well-being around age 30. Senior author Andrew Oswald says the results show a midlife crisis is normal. So relax.